System of distribution



June 11, 1929. l HEWLETT 1,717,211

SYSTEM OF DISTRIBUT'ION Filed June 1, 1927 Inventor:

Edw ard M. Hewlett 'H as Attorney 7 Patented June 11,1929.

UNITED STATES PATENT OFFICE.

EDWARD M. HEWLETT, OF SOHENECTADY, NEW YORK, ASSIGNOB 'I'O GENERAL ELECTRIC COHPANY, A CORPORATION 01' NEW YORK.

SYSTEM OF DISTRIBUTION.

Application filed June 1,

1 -have been suggested and used for many purposes and it is often desirable to provide means for energizing the electron emitting electrode of these devices in accordance with the current in the circuit with which the device is associated in order to eliminate auxiliary constant potential devices or expensive potential transformers in case the device is used in connection with a high potential circuit. My invention is particularly suitable for use in connection with electron discharge devices adapted for power conversion and control of the type disclosed and claimed in application Serial No. 594,370 of Albert W. Hull, filed October 13, 1922, and assigned to the same assignee as this application.

An object of my invention is to provide an improved arrangement comprlsing current responsive means associated with a circuit normally carrying current for heating the electron emitting electrode of an electron discharge device.

A further object of my invention'is to provide an improved arrangement for supplying heating current of substantially constant value to an electron discharge device of the hot cathode type from a circuit normally traversed by a variable current.

My invention will be better understood by reference to the following description taken inconnection with the accompanying drawin' in which the single figure diagrammatica ly illustrates one embodiment of my vention, and its scope will be pointed out-in the appended claims.

In'the drawing, my inventionhas been shown in connection with an electron discharge device of the type adapted for use as an automatic cut-out device in connection with a load circuit which is arranged to be energized from a power transmission circuit, but it will be apparent that my invention is equally well adapted for use with. electron discharge devices of this type used in the rectification of high potential circuits. the discharge of lightning, and like technical pur- 1927. Serial No. 195,806.

poses in systems of distribution. An alternating current circuit comprising conductors 1 and 2 represents a main circuit of a power transmission system energized by an alternating current generator 2 supplying energy to a main load circuit comprising translating devices 3 beyond a subsidiary load circuit 3 comprising translating devices 4. The load circuit 3 is connected to the conductors 1 and 2 by means of a transformer 5 and thermionic vacuum tubes 6 and- 7. The thermionic tube 6 is of the two-electrode type comprising a cathode 8 and an anode 9 enclosed in a suitable envelope 10 containing an inert gas such as argon at a lowpressure. Similarly,

thermionic tube 7 comprises a cathode 11.

and an anode 12 enclosed in a suitable envelope 13. The cathode material of cathodes 8 and 11 is preferably of the thoriated refractory metal type, for example, thoriated tungsten such as is disclosed and claimed in Letters Patent No. 1,244,216, granted to Irving Langmuir, October 23. 1917, and assigned to the same assignee as this application.

In accordance with my invention, the oathode of tube 6 is excited by means of a transformer 14 comprising a primary winding 15 connected in series with the main conductor 2 and a secondary winding 16 which is connected across terminals of the cathode electrode or filament 8. Similarly, the cathode of thermionic tube 7 is excited by means of a transformer 17 comprising a primarywinding 18 connected in series with the supply conductor 2 and a secondary winding 19 which is connected across the terminals of the cathode electrode or filament 11. The transformers 14 and 17 are arranged to be magnetically saturated at the minimum load current of the main power circuit so that the cathode excitation is substantially constant for any load current in the power circuit above the normal minimum value.

The thermionic tubes 6 and 7 are arranged to pass both waves of alternating current from the main circuit to the load circuit so that alternating current flows in the load circuit 3. While this arrangement is particularly useful and the preferred arrangement for energizing load circuits at isolated points along a transmission line, various modifications comprising a single tube acting to pass a half wave of alternating current or two tubes arranged to provide full wave rectification will occur to those skilled in the art, and

may be used if preferred without departing from my invention in its broader aspects.

In the arrangement shown, the connection of one tube is reversed from the usual arrangement of two tubes of the two-electrode type which are'connected for full wave rectification. In other words, one tube passes the positive wave of alternating current but blocks current of the negative wave, while the other tube passes the current of the negative wave and blocks current of the positive wave. Anode 9 of thermionic tube 6 is connected to conductor 1 of the main circuit through the primary of transformer 5. The cathode of this same tube is connected to conductor 2 of the main circuit from the midpoint of the secondary winding 16 of its exciting transformer 14. On the other hand,

anode 12 of thermionic tube 7 is connected to conductor 2 of the main circuit, and the cathode 11 is connected to conductor 1 of the main circuit through theprimary of transformer 5 from the midpoint of secondary winding 19 of the exciting transformer 17 If conductor 2 for the instant is considered positive, conductor 1 is considered negative, and current flow through the tube is considered to be from the cathode to the anode, current will flow from the conductor 2 through the secondary of transformer 16 through the cathode 8 to the anode 9 through the primary winding of transformer 5 back to the conductor 1. On this positive wave current can not pass through tube 7 Now,

if we assume reversed polarity of conductors 1 and 2, current will flow from conductor 1 through the primary of transformer 5 through \the secondary winding of transformer 19, the' cathode 11 of tube 7, to the anode 12, and thence to the negative conductor 2. On the negative wave current can not pass through the tube 6. Hence, it will be 0 vious that the arrangement of the two tubes permits an alternating current to flow in the load circuit since one tube passes current of the'positive wave and blocks current of the negative wave, while the other tube passes current of the negative wave and blocks current of the positive wave.

In the circuit to the load circuit 3, I pro-,

vide. a circuit interrupter 20 which for purposes ,of illustration is shown to indicate an under-load relay having contacts connected directly in the circuit for interrupting the circuit after the tubes have operated in a manner to be described hereinafter. The relay, as shown, comprises an operating coil 21 having a plunger 22 which carries contacts 23 and 24 arranged to introduce a break in each side of the circuit to the transformer when the current through coil 21 falls below a predetermined value.= The relay contacts are moved to the circuit closing position by any convenient operating means which is indicated by the hand operating means 25.

Hence, a tube having a thoriated filament cathode may be operated-to pass an appreciable current, but if the film of thorium material is disintegrated and the cathode is still operated at the same temperature, it will pass appreciably less current.

In the particular arrangement shown, I utilize this phenomenon to interrupt the flow of current in theload circuit. The heating temperature of the cathode is maintained at a substantially constant value irrespective of the variation of current in conductors 1 and 2. Since the tubes contain an inert gas such as argon, violent ionization takes place in the tube when the current therethrough or the potential difference between the cathode and anode exceeds a predetermined value. With the increased ionization the ionized gas travels to the anode, being positive, and the positive nuclei travel to the cathode and subject it to a severe bombardment which is sufiicient to disintegrate the filmvof thorium material on the surface of the filament. As soon as this surface film of thorium material is disintegrated the electron emission from the cathode which is still excited by the same current and is approximately at the same temperature, falls off appreciably, in fact to such an extent that the tube cannot pass appreciable current.

The operation of the embodiment, of my invention shown is substantially as follows: Starting with the various instrumentalities in the positions indicated in the drawing and the power circuit carrying a current above the minimum value necessary to saturate the series transformers 14 and 17 the thermionic tubes 6 and 7 will be in a condition to pass current. The switching device 20 is moved to a circuit closing position by means of the hand operating device 25 and a circuit is completed from the main circuit through the tubes, the contacts 23 and 24 of the switch 20, to the primary of transformer 5. As soon as current above a predetermined value flows to the load circuit 3 the switching equipment will be maintained in its circuit closing pofalls below the pick-up value of coil 21, the contacts 23 and 24 will be moved to a circuit interrupting position and the load circuit will be disconnected from the main circuit.

The under-load relay is not absolutely necessary in the particular arrangement shown. It renders the load circuit safe against potential to ground when the tubes have operated to interrupt the current flow. In the particular type of electron discharge device shown the surface film is removed by bombardment and requires only removal of the condition causing bombardment to cause substantially instant restoration of the film. If switch 20 is moved to its circuit closing position, operation may be resumed if the overload or short circuit condition has been removed.

While I have shown and described a parbe obvious to those skilled in the art that various changes and modifications may be made without departing from my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

\Vhat I claim as new and desire to secure by Letters Patent of the United States, is

1. In a system of distribution, an electric circuit normally traversed by a current varying in magnitude, a load circuit, an electron discharge device having a thermionic cathode for interconnecting said circuits, said cathode having a surface film of higher emission at a given temperature than the body of said cathode and sufiiciently sensitive to positive ion bombardment to decrease substantially the current carrying capacity of said discharge device when currents above a predetermined value traverse said tube, and means comprising a transformer connected in series relation with said electric circuit for heating said cathode with a substantially constant current when the current traversing said electric circuit is above a predetermined value.

2. In a system of distribution, an alternating current circuit normally traversed by current iarying in magnitude, a load circuit, a transformer comprising a primary winding and a secondary winding, said secondary Winding being connected to said load circuit, two electron discharge devices of the hot cathode type connected in series relation between said alternating currentcircuit and the primary winding of said transformer and adapted to interrupt the circuit therebetween when the current through said devices exceeds a predetermined value, said electron discharge devices being adapted to energlze sald transformer with alternating current,

a switch having contacts for completing each side of the circuit to said transformer, means responsive to the current supplied to said load circuit above a predetermined value for maintaining said switch in its circuit closing position, and a transformer connected in series relation with said alternating current circuit and adapted to be magnetically saturated at a predetermined current for energizing the cathode of said electron discharge devices -witha substantially constant current.

In witness whereof, I have hereunto set my hand this 31st day of May, 1927.

EDWARD M. HEWLETT 

